Super cooler for a heat producing device

ABSTRACT

A super cooler device including a thermo electric cooler on a digital micro mirror device.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of and claims priority to U.S. application Ser. No. 09/780,025, filed Feb. 9, 2001, which claims priority to U.S. application Ser. No. 60/181,530 filed Feb. 10, 2000.

SUMMARY

[0002] The present application relates to cooling of a heat producing device, using a thermoelectric cooler arranged as a super cooler. More specifically, the present application teaches cooling of a device, such as a digital mirror device, which requires a specified temperature gradient across the device, using a supercooled element.

BACKGROUND

[0003] Electronic devices often have specified cooling requirements. One device that has specific cooling requirements is a digital micromirror device (“DMD”) available from Texas Instruments (“TI”). The manufacturer of this device has specified a maximum overall temperature for the device and also a specified maximum temperature gradient between the front and rear faces of the device during operation.

[0004] For example, the temperature of the specific DMD used in this application needs to be kept below 55° C., however, in this application it is desirable to keep the device at or below ambient. This may allow operation in an ambient environment up to 55° C., such as may be encountered in a stage theater or studio environment. The temperature differential between the front and rear of the DMD cannot exceed 15°. Besides the heat from the operation of the DMD itself, large amounts of heat from a high intensity light source must be dissipated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] These and other aspects will now be described in detail with reference to the accompanying, wherein:

[0006]FIG. 1 shows an exploded diagram of the parts making up the supercooler assembly;

[0007]FIG. 2 shows the rear of the DMD and parts which are assembled to the DMD;

[0008]FIG. 3 shows a circuit for driving a thermoelectric cooler; and

[0009]FIG. 4 shows a flowchart of operation.

DETAILED DESCRIPTION

[0010] According to the present system, a “supercooler” device, is used to monitor and control the temperature of a device which can control light on a pixel-by-pixel basis, e.g. a digital mirror device (DMD).

[0011] The mechanical structure of the supercooling assembly is shown in FIG. 1. The pixel element is a DMD 99, which forms part of a DMD assembly 100. As shown, a thermal connection 105 to the DMD 99 is provided.

[0012] A cold plate 120 is assembled to a mounting bracket 110 in a manner which allows minimal thermal transfer between the two components. The DMD is attached directly to the cold plate 120, hereby allowing maximum thermal transfer between the DMD and cold plate 120, but minimal thermal transfer to the mounting bracket 110. The rear surface of the cold plate 120 is directly connected to one side of the thermoelectric device 130, and the other side of the thermoelectric device is connected to a heat sink/fan assembly 140.

[0013] Insulating foam gaskets are fitted around the DMD rear stud, the cold plate, and the thermoelectric device in order to isolate them from the outside ambient air. This improves the efficiency of the cooling system by eliminating the effects of condensation and properly controlling the flow of heat from the DMD to the cold plate, through the thermoelectric device, and into the heat sink/fan assembly.

[0014] The thermoelectric cooler element 130 operates as conventional to produce one cold side 131 and one hot side 132. The hot side is coupled to the heat sink/fan-assembly 140 to dissipate the heat. In a preferred mode, the heat sink/fan assembly is columnar is shape, with a substantially square cross section. This facilitates using a square shaped fan housing 142. The square shaped fan unit allows the maximum use of the space for a fan, whose blades usually follow a round shape. Any type of cooling fan, however can be used.

[0015] The DMD assembly 100 has an extending rear stud 105 which is covered with thermal grease. This stud extends though a hole 112 in the bracket assembly 110.

[0016] The plate 120 is actively cooled, and hence becomes a “cold plate”. The active cooling keeps the metal plate at a cooled temperature, and the thermal characteristics of the plate material allow the heat flowing into the plate from the DMD to be evenly distributed throughout the entire plate. The plate is preferably about ¼″ to ⅜″ in thickness, and of comparable outer size to the thermal contact area of the thermoelectric cooler element 130. This allows the localized and concentrated heat at the rear stud of the DMD to be evenly dissipated through the cold plate and then efficiently transferred through the full surface area of the thermoelectric cooler element. As shown, the assembly employs thermal insulation techniques such as fiber/plastic sleeves and washers in the mounting of components, in order to prevent heat transfer via mounting screws etc. Since this heat transfer could be uncontrolled, it could otherwise reduce the cooling efficiency.

[0017] The front of the DMD is shown in FIG. 2. Temperature sensor 200 is mounted to have a fast response to temperature changes. A second temperature sensor 122 is mounted to the cold plate 120 and effectively measures the temperature of the rear of the DMD 99. This second temperature sensor 122 therefore monitors the back temperature.

[0018] The hot side 132 of the thermoelectric cooler is coupled to a heat sink assembly 130. The heat sink assembly 140 includes a heat sink element 140. As shown, the device has fins and a top-located cooling fan 142.

[0019] A block diagram of the control system is shown in FIG. 3. Controller 300 operates in a closed loop mode to maintain a desired temperature differential across the sensors 122, 200.

[0020] One important feature of the present application is that the thermoelectric cooler is controlled to maintain the temperature of the DMD at the desired limits. These limits are set at a target of 16° C. on the front, and a differential no greater than 15° between front and rear. The thermoelectric cooler is controlled using very low frequency or filtered pulse width modulation. In a first embodiment, the controlling micro controller 300 produces an output 302, e.g., digital or analog. This drives a pulse width modulator 304. The output of the pulse width modulator is a square wave 306 or a signal close to a square wave, with sufficient amplitude and power to produce the desired level of cooling down the thermoelectric cooler. The square wave is coupled to an LC filter 308 which has a time constant effective to smooth the 20 KHz switching frequency. The output to the thermoelectric cooler is therefore a DC signal. This drives the thermoelectric cooler 130 and causes it to produce a cooling output. In a second embodiment, the LC filter is removed and the TEC is driven directly by the square wave 306 at a lower frequency, e.g. 1 Hz.

[0021] The microcontroller operates according to the flowchart of FIG. 4. Step 400 determines if the temperature of the first temperature sensor T1 is greater than 16°. If so, the output to the TEC remains “on”, resulting in further cooling. When the temperature falls below 16°, the drive to the TEC is switched off. The sample period is approximately ½ second between samples.

[0022] At 410, the system checks temperature of the first sensor (T1) and of the second sensor (T2) to determine if the differential is greater than 15°. If so, the output is switched “on”. Step 420 indicates a limit alarm, which represents the time of increase if the rate of change continues. If the rate of change continues to increase, as detected at step 420, a fault is declared at step 425. This fault can cause, for example, the entire unit to be shut off, to reduce the power and prevent permanent damage.

[0023] Other embodiments are contemplated. 

What is claimed:
 1. An apparatus, comprising: a temperature sensing device, monitoring a front temperature of a front surface of a first driven device, and a rear temperature related to a rear surface of the first driven device; a controller, detecting both a temperature of the first driven device and a temperature differential across the first driven device; a thermoelectric cooler, coupled to actively cool the first driven device under control of said controller; and wherein said controller produces outputs which control both overall temperature of the first driven device and temperature differential of the first driven device.
 2. An apparatus as in claim 1, wherein the first driven device is a digital mirror device.
 3. An apparatus as in claim 1, further comprising a lighting projector, projecting light on said front surface of said first driven device.
 4. An apparatus as in claim 1, further comprising a pulse width modulated device, driven by said controller, to produce a pulse width modulated output to drive said thermoelectric cooler.
 5. An apparatus as in claim 4, wherein said pulse width modulated output is applied directly to said thermoelectric cooler.
 6. An apparatus, comprising: a digital micro mirror device assembly, including a digital micro mirror device mounted thereon; and an active cooling unit, coupled to cool said digital micro mirror device.
 7. An apparatus as in claim 6, wherein said active cooling unit includes a thermoelectric cooler.
 8. An apparatus as in claim 7, further comprising a temperature sensor, sensing a temperature of said digital micro mirror device, and a controller, controlling said thermoelectric cooler based on the sensed temperature.
 9. An apparatus as in claim 8, wherein said temperature sensor includes a first temperature sensor sensing a temperature near the front of the digital micro mirror device, and a second temperature sensor sensing a temperature near the rear of the digital micro mirror device.
 10. An apparatus as in claim 9, wherein said controller operates to control the thermoelectric cooler based on both the front temperature, and a difference between the front and rear temperatures.
 11. An apparatus as in claim 6, further comprising a controller for said active cooling unit, said controller controlling production of a pulse width modulated signal that controls the active cooling unit.
 12. An apparatus as in claim 10, further comprising a controller for said active cooling unit, said controller controlling production of a pulse width modulated signal that controls the active cooling unit.
 13. An apparatus as in claim 6, further comprising a plate formed of heat distributing material, coupled to said digital micro mirror device assembly and said active cooling unit, and of a size which is affective to evenly distribute heat from the digital micro mirror device assembly into said plate.
 14. An apparatus as in claim 13, further comprising a temperature sensor, sensing a temperature of said digital micro mirror device, and a controller, controlling said thermoelectric cooler based on the sensed temperature.
 15. An apparatus as in claim 14, wherein said temperature sensor includes a first temperature sensor, sensing a temperature near a front of the digital micro mirror device, and a second temperature sensor sensing a temperature of said plate, and wherein said controller operates both on said front temperature, and based on a difference between said front and said rear temperature. 